Objective: Our goal is to reduce the incidence of venous thromboembolism in the elderly. This project will be a comprehensive secondary analysis an existing data set to determine the incidence of thromboembolic complications in the first 3 months following a wide variety of different operations (n=approximately 60) and a wide spectrum of medical illnesses (n= approximately 30). Background: The majority of patients who develop deep-vein thrombosis (DVT) or pulmonary embolism (PE) are over the age of 60 years and recovering after major surgery or a major medical illness, particularly those with a malignancy. Most of the literature regarding the incidence of DVT after surgery actually refers to the incidence of asymptomatic venous thrombosis. We want to analyze the incidence of newly diagnosed DVT and PE within 3 months following a wide spectrum of different operations/illnesses to determine: 1) which operations or illnesses are associated with the highest rates of DVT and/or PE, 2) the effect of age as a risk factor for developing symptomatic DVT and PE, 3) the effect of race/ethnicity, and 4) the proportion of all thromboembolic complications that occur after hospital discharge. Methods: Using a large data set with linked records provided by the State of California (years 1993-1996), we will: 1) systematically select major illnesses and operations primarily affecting the elderly from the 25 major disease categories in the Diagnostic Related Groups, 2) select ICD-9-CM codes to precisely define the cohorts of interest, 3) determine the number and time of DVT and PE events, 4) create Kaplan-Meier plots of the 3 month cumulative incidence of thromboembolic events for each condition, 5) calculate the directly standardized (to California 1990 census) 3-month cumulative incidence of thromboembolic outcomes for each operation/condition, and 5) determine the effect of age by stratified analysis of the data (grouping ages = 55-64, 65-75, 76-up) as well as proportional hazards regression (or logistic regression) modeling, controlling for sex, race and malignancy. Implications. If it can be shown that: 1) certain previously unsuspected operations and medical illnesses are associated with high rates of clinical thromboembolic events, particularly among the elderly, and 2) if further case-control studies show a low prevalence of thromboprophylaxis among cases hospitalized for these operations/conditions, the findings will provide strong evidence that these patients should be treated more aggressively with thromboprophylaxis.